This invention relates to bearings, and more particularly to pin bearings, such as are used in the pivotal connections in a piano action; that is, the centers on which the wooden action members pivot.
The pivotal connections in a piano action must be durable, low in friction yet firm, have with little side-play, and be quiet in operation. These connections are usually effected with a tongue-and-fork arrangement held together by means of a lateral or transverse pin, usually made of "nickel silver" to eliminate corrosion, and are manufactured to precise tolerances as to diameter, length, and concentricity. The pin is held firmly in the central or tongue member, and the fork member is provided with a bushing with a view toward achieving a noiseless, efficient and durable action.
For many years the bearings, or bushings, for these centers have been formed from a woven wool cloth, a special all-wool felted fabric especially designed and manufactured for the purpose (known in the art as bushing cloth) by a number of manual operations. The cloth is first dipped in water to allow it to shrink and after drying is severed into strips of a width somewhat less than the circumference of the bushing holes. The strips thus formed are then pulled through the holes of the bearing-containing parts, such as the bifurcated fork element having axially aligned bearing holes in its bifurcations, the cloth becoming circumferential in the bearing holes. Glue is then applied to the cloth along one outboard side of the bifurcated member, and the member then pulled over the glue-wetted portion. The member is then cut away from the cloth strip at the outer faces of its bifurcations, and the length of the strip between the bifurcations is also cut away and discarded; thus, only a small portion of the bushing cloth is used.
The wool felted fabric has sufficient resiliency and softness to substantially eliminate noises, but to be durable and firm, the bearing must be dense. Furthermore, the bushing holes in the bearings must be aligned for low friction operation of the shaft or center pin placed therein. Heretofore, the problems of durability and smooth operation have been addressed by employing a wool felt which is initially much thicker than its ultimate dimension in the bearing, and then carrying out the further manual operations upon the cloth glued in the member as described above. To provide openings for the center pin, the tight cylinders of bushing cloth in a bearing member, after the glue holding them therein has hardened, are opened preliminarily along the axis of the bearing formation. Following this a metal pin of the diameter of the center pin is driven with a forward motion into the preliminary opening, radially compressing the cloth cylinders to a considerably denser condition. With the rod inserted, the assembly is then dipped in water for a short time to permit the wool cloth cylinders to absorb moisture, and the assembly is allowed to dry before removing the pin. Wool of course absorbs water appreciably and if unopposed will swell with moisture absorption. However, under the described confined condition the wool cylinders are substantially prevented from altering their dimensions due to moisture absorption, and are, therefore, forced to a denser condition and upon drying are "set" to this condition. Finally, upon removal of the metal pin the assembly is ready for use in a bearing combination, with center pin holes in the wool cylinders formed to a size adapted to a particular metal center pin and in alignment brought about by the straight compression pin.
Although bearings fabricated as described have proven to have resilience and softness sufficient to eliminate noises, and appropriate density to be durable and firm under the impacts imposed in the playing of a piano, under continued use in certain atmospheric conditions the bearing tends to deteriorate, with attendant loss of its desirable properties. The felted wool being hygroscopic, it tends to swell in moist atmospheric conditions and to shrink in dry conditions. Consequently, under moist conditions the center may become so tight as to interfere with the functioning of the pivotal connection, and the corresponding piano key either loses all speed and sensitivity of action or fails to function entirely. A common "fix" for malfunctions due to tightening of the center because of high humidity is the application of a drop of a solvent such as benzene, or an alcohol and water mix, which usually relieves the pivot only temporarily in that it tends to tighten up again with continued exposure to moist conditions. Conversely, with dry conditions the centers occasionally become too loose, resulting in rattles in the action and inaccuracy in the alignment of parts, with consequent loss of power and control in the so-called "touch qualities" of the action.
Over the years there have been many attempts to improve the bearings of piano actions, either by use of materials other than felted wool for the bushing or by simplifying and reducing the cost of the labor-intense fabrication of the centers. For example, Knoblaugh U.S. Pat. Nos. 2,580,436, 2,580,437 and 2,580,438 describe bearing assemblies in which the bushing is in the form of a braided tubular sleeve comprised of many braid elements in the form of cords, tight yarns, or thread which may be textile material such as wool or silk, but preferably nylon thread. A braided sleeve of appropriate size is placed under tension and coated with a material of a type which dries and hardens to a suitable tensile strength, such as a nitrocellulose lacquer cement applied in an amount such that upon drying the completed tube has an outside diameter such that tube fits snugly in a bearing hole in the bifurcated bearing member. Thus, the prepared bearing material comprises a stiff tube which may be pushed into a bearing hole, and as part of the assembly operation a cement is applied to the external surface for attaching the bearing material to the wood bifurcated member of the action.
Another approach, which has been used by applicant's assignee for several years, was to eliminate the use of bushing cloth altogether and replace it with a one-piece bushing formed of a suitable plastic or elastomeric material, such as Teflon. The bushing has an intergral annular flange at one end which bears against the internal or tongue side of each arm of the bifurcated member, and is inserted from the inside into a bushing hole of correct size to afford a light push fit, so as to eliminate any possible distortion of internal diameters. An initial version of this type of bushing is described in U.S. Pat. No. 3,240,095, and a refinement thereof wherein the exterior surface of the bushing has a "barrel shape" to provide self-alignment of the bushing with the bearing pin regardless of misalignment of the bushing holes in the respective fork arms, is described in U.S. Pat. No. 3,942,403. Although the performance of piano actions with this type of bushing has been sufficiently good to have been used in preference to bushing cloth for some twenty years by applicant's assignee, this long-term experience has demonstrated that it is not without fault, and lacks some of the desirable properties of wool felt. For example, in spite of observance of usual care in the fabrication of the wooden parts of the piano action, the drilled holes in the two fork arms may not be perfectly aligned, or may be misaligned with the drilled pin-receiving hole in the tongue part, with the consequence that the internal bores of the two bushings, when inserted with a push fit in the drilled holes in the fork arms, are likewise misaligned with the bearing pin, thus causing the pin to bind in the bushing and not rotate with the desired ease. This problem is compounded by the sizing of the bushing relative to the size of the holes in the fork arms to afford a light push fit, so as to eliminate any possible distortion of the internal diameter of the bushing and to increase the effective length of the contact between the bearing pin and the internal bore of the bushing. Also, it has been found difficult to maintain the clearance between mating wood parts to tolerances sufficient to allow the center to work freely when the wood parts are distorted by extreme conditions of moisture and/or temperature; under certain conditions there is an excess of freedom which causes the action to be noisy, and under other conditions the pin tends to bind in the bushing and does not rotate with the desired ease. In short, although the one-piece bushing reduces the labor cost of manufacture of the piano action and under favorable operating conditions provides acceptable performance, under other conditions it lacks the desirable qualities of the long-used wool bushing cloth.
Other piano manufacturers have continued to use felt bushings in their piano actions, modified in various ways to obviate some of the problems discussed earlier. For example, the surface of the felt ring has been coated with silicone or impregnated with suds or soapy water to reduce friction between the bushing and bearing pin; however, a bearing assembly of this construction has the drawback that it will lose lubricity during long use. U.S. Pat. No. 3,730,963 proposes as a solution to this problem the use of a bushing cloth consisting of a fabric woven from mixed spun yarns of wool fibers and carbon fibers which are napped on the surface of the fabric to provide high and long-term lubricity.
In view of the virtues of wool felt as a bushing in a piano action, as demonstrated by its use over a very extended period, albeit not without the weaknesses and shortcomings outlined above, the present invention seeks to provide bearings utilizing wool felt which in some respects simplifies their fabrication as compared to the existing practices outlined above and which has considerably improved bearing qualitities which are maintained during long use and exposure to a wide range of atmospheric conditions. Accordingly, the object of this invention is to provide a construction and method of fabricating the same for supporting the rotatable parts of a piano action mechanism which retains the desirable qualities of wool felt as a bushing material during long use, which is minimally affected by changes in atmospheric conditions, and which retains a desired lubricity during long use.